Chemistry Reference
In-Depth Information
Mitochondria
Cytoplasm
[SO
4
]
2-
H[PO
4
]
2-
Damaged RNA
Nucleus
Cr(VI)
Cr(VI)
Cr(VI)
Cr(III)
Reduction
Intermediates
???
Intermediates
{Cr(V), Cr(IV),
radicals}
???
Damaged
DNA
Intermediates
Cr(III)
Reduction
pH 3-4.5
Cr(III)
Cr(III)
Acidic
Vacuole
Phagocytosis
Insoluble
Chromate
Figure 6.7.
An overview of Cr redox chemistry in biological systems (adapted from
Codd et al. [44] with the permission of Elsevier Inc.).
(DMPO) and α-(4-pyridyl-1-oxide)-N-t-butylnitrone (POBN), have been
applied extensively to establish the formation of Cr(V) and
•
OH radicals in
the reductions of Cr(VI) using reductants such as ascorbate, cysteine, pencil-
lamine, GSH, and NAD(P)H-dependent flavoenzymes (e.g., GSH reductase
and lipoyl dehydrogenase) [27, 122, 129, 131-137]. A close relationship between
the formation of organic radicals and the species of Cr(V)/Cr(IV) in the reduc-
tion of Cr(VI) has been determined [96]. The reactive species such as free
radicals
O
−
and
•
OH may effectively be produced from the reaction of Cr(VI)
with biological reductants [131, 132]. The possible reactions to produce such
species are as follows:
•
(6.37)
Cr VI RH Cr V R
(
)
+
→
(
)
+
•
(6.38)
Cr VI RH Cr IV R
(
)
+
→
(
)
+
2
(6.39)
R O
•
+ → +
2
R O
−
−
+
.
(6.40)
2
O
+
2
H
→
H O O
+
2
2
2
2
Cr(V) and Cr(IV) produced in reactions (6.37) and (6.38) may be further
involved in Fenton-like reactions to yield
•
OH radicals (reactions 6.41 and
6.42):
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